In recent years, it is proposed that, regarding power supply to residences and buildings among other things, supply control of the power is performed using IT (information technology) technology and that power storage system in addition to the grid power from a power plant is used. For example, Patent Document 1 discloses disposing photovoltaic power generator and a power storage system in a residence, outputting power from the photovoltaic power generator to an external power system, and using the power for charging the power storage system.